1. Field
This disclosure relates to projectiles and in particular to increasing the range of projectiles.
2. Description of the Related Art
Any object moving through air is subject to various forces that act in a direction opposed to the direction of motion and thus tend to retard the motion. One such first commonly called “base drag” which is the force caused by a low pressure region formed behind a moving object. In oversimplified terms, the moving object leaves a partial vacuum in the space that the object has just vacated. Base drag is particularly severe for objects, such as projectiles and trucks, which end abruptly with a rear surface roughly normal to the direction of motion.
The base drag of projectiles may be reduced by increasing turbulence near the rear of a projectile such that the adjacent air fills the space being vacated by the moving projectile more quickly. U.S. Pat. No. 6,297,486 and U.S. Pat. No. 4,813,635 describe projectiles with features intended to reduce base drag.
The base drag of projectiles may be reduced or eliminated by filling the space being vacated by the projectile with gas generated within the projectile. U.S. Pat. No. 6,297,486 and U.S. Pat. No. 4,813,635 describe projectiles that burn a fuel material to produce gas that is exhausted through the base of the projectile to reduce base drag. This approach to reducing base drag is commonly referred to as “base bleed”. The addition of a base bleed generator to a projectile increases the projectile cost and, due to the need to store the base bleed fuel, reduces the volume within the projectile that is available for other content.
Virtually all modern munitions are required to be “insensitive”. Insensitive munitions are munitions that minimize the probably of inadvertent ignition or detonation, and which minimize the severity of collateral damage to weapons platforms, other equipment and personnel if inadvertent ignition should occur. Specifically, insensitive munitions are munitions that do not react more violently than burning when subjected to slow or fast heating; fragment, bullet, spall, or shaped charge impact; or detonation of an adjacent similar motor. Requirements for insensitive munitions are generally described in MIL-STD-2105B, Hazard Assessment Test for Non-Nuclear Ordinance. Specific test requirements are described in NATO STANAG (Standardization Agreement) documents.
Significantly, base bleed generators typically generate gas using fuel materials that are slow burning but easily ignitable. The use of easily ignitable base bleed fuel materials may complicate or preclude the projectile from complying with various insensitive munitions requirements.
Base drag may also be reduced by modifying the shape of the rear of the moving object. U.S. Pat. No. 4,674,706 describes a projectile including a telescoping extension to reduce base drag at the rear of the projectile. U.S. Pat. No. 6,657,174 describes a projectile including an inflatable extension to reduce base drag at the rear of the projectile.
Throughout this description, each element appearing in a figure is assigned a unique three-digit reference designator, where the most significant digit is the figure number where the element was introduced. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.